Park7 Expression Influences Myotube Size and Myosin Expression in Muscle

Hui Yu,Jolena N Waddell,Shihuan Kuang,Christopher A Bidwell,Makoto Kanzaki

doi:10.1371/journal.pone.0092030

Hui Yu, Jolena N Waddell + Show 3 more

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https://doi.org/10.1371/journal.pone.0092030

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Abstract

Callipyge sheep exhibit postnatal muscle hypertrophy due to the up-regulation of DLK1 and/or RTL1. The up-regulation of PARK7 was identified in hypertrophied muscles by microarray analysis and further validated by quantitative PCR. The expression of PARK7 in hypertrophied muscle of callipyge lambs was confirmed to be up-regulated at the protein level. PARK7 was previously identified to positively regulate PI3K/AKT pathway by suppressing the phosphatase activity of PTEN in mouse fibroblasts. The purpose of this study was to investigate the effects of PARK7 in muscle growth and protein accretion in response to IGF1. Primary myoblasts isolated from Park7 (+/+) and Park7 (−/−) mice were used to examine the effect of differential expression of Park7. The Park7 (+/+) myotubes had significantly larger diameters and more total sarcomeric myosin expression than Park7 (−/−) myotubes. IGF1 treatment increased the mRNA abundance of Myh4, Myh7 and Myh8 between 20-40% in Park7 (+/+) myotubes relative to Park7 (−/−). The level of AKT phosphorylation was increased in Park7 (+/+) myotubes at all levels of IGF1 supplementation. After removal of IGF1, the Park7 (+/+) myotubes maintained higher AKT phosphorylation through 3 hours. PARK7 positively regulates the PI3K/AKT pathway by inhibition of PTEN phosphatase activity in skeletal muscle. The increased PARK7 expression can increase protein synthesis and result in myotube hypertrophy. These results support the hypothesis that elevated expression of PARK7 in callipyge muscle would increase levels of AKT activity to cause hypertrophy in response to the normal IGF1 signaling in rapidly growing lambs. Increasing expression of PARK7 could be a novel mechanism to increase protein accretion and muscle growth in livestock or help improve muscle mass with disease or aging.

Highlights

Callipyge sheep exhibit postnatal muscle hypertrophy, with higher rates of protein accretion and lower rates of fat deposition compared to normal sheep [1,2]
Semimembranosus and supraspinatus muscle samples were collected from 3 callipyge and 3 normal lambs at 30–35 days of age when muscle hypertrophy is detectable by muscle mass
This study focused on Park79s effect on AKT phosphorylation due to its prominent role in regulating muscle growth, other reported biological activities in oxidative stress, anti-apoptosis and several regulatory pathways [17,18,19,20,21,29,30,31,32] may contribute to improved muscle growth

Summary

Introduction

Callipyge sheep exhibit postnatal muscle hypertrophy, with higher rates of protein accretion and lower rates of fat deposition compared to normal sheep [1,2]. The callipyge mutation is a single nucleotide polymorphism in the DLK1-DIO3 imprinted gene cluster [7,8] that causes up-regulation of Delta-like 1 (DLK1) and Retrotransposon-like 1 (RTL1) in hypertrophied muscles [9,10,11,12,13]. Transgenic mice over-expressing Dlk exhibited increased muscle mass and myofiber diameter [14]. Muscle-specific gene ablation of Dlk in the mouse resulted in reduced body weight and skeletal muscle mass due to reductions in myofiber numbers [15]. Over-expression of Dlk in culture was shown to inhibit myoblast proliferation and enhance myotube differentiation [15]

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